Ink jet printers create characters by ejecting individual droplets of ink that combine to form letters, numbers or symbols on a target or substrate. These printers normally consist of an ink source; a print head which contains the ink and physically ejects the ink droplets onto the substrate or object; and a controller which dictates the individual locations where the droplets are ejected.
A typical print head consists, in part, of an ink jet nozzle and two electrically charged plates. The electrically charged plates are parallel to one another, and separated by a small distance. The ink jet nozzle ejects single drops of electrically charged ink that travel between the two electrically charged plates on their way to the substrate. The electrical charge on the two plates develops a magnetic flux between the plates. As each ink drop leaves the nozzle, it is typically imparted with a particular voltage, which can vary between approximately -12 volts and approximately +300 volts. Depending on the charge on a particular electrically charged ink drop, it will be attracted toward one of the plates. If there is no attraction by either plate, the ink drop will travel parallel to the two plates. If the ink drop is positively charged, then it will be attracted toward the negatively charged plate, and its path will curve toward that plate. In this manner, the ink drop will strike the substrate closer to the attracting plate and further from the other plate. By varying the electric charge on the ejected ink drop, the drop may be directed to strike the substrate anywhere along an imaginary line on the substrate that is perpendicular to both of the plates.
In this arrangement, if both the substrate and the printer head are fixed with respect to one another, then the print head would only be able to print a row of dots on the substrate that combine to form a line perpendicular to both electrically charged plates. For the printer to be able to form letters, it is therefore necessary to have the substrate move in relation to the print head (or vice versa).
The printer forms a letter or other symbol by ejecting drops in vertical "slices" as the object to be printed on moves in front of the print head. These slices are simply drops of ink selectively placed on the imaginary vertical line between the plates, in locations which correspond to a portion of the letter or other symbol. As the print medium moves, vertical slices are printed directly adjacent to one another. Each vertical slice is called a stroke, and combines with each adjacent stroke to form a letter, character or other symbol.
The typical commercial printing arrangement fixes the print head alongside a moving substrate, or along a conveyor belt which transports objects to be printed on past the print head. As the substrate or object moves, the print head ejects droplets of ink, forming characters. Print heads are well known to those skilled in the art of printing systems. A typical ink jet printer head, on sale for several years, has already been described above.
A number of printing systems that use ink-jet printers are also known in the art. However, the inventors of the subject invention are not aware of any system that allows a single computer to control multiple ink jet printers through a single interface. Nor are the inventors aware of an ink jet printing system that is capable of printing in a direction other than the substrate or conveyor length, when the "length" refers to a direction parallel to the direction in which the substrate or conveyor travels. For example, the inventors know of no system capable of printing along a width, where the width refers to a direction perpendicular to and in the same plane as the substrate's line of travel; when the printers are to print on objects moving along a conveyor belt, the "width" refers to either (1) a direction perpendicular to the conveyor belt's line of travel in a plane parallel to the plane formed by the conveyor belt, or (2) a direction perpendicular to the plane formed by the conveyor belt. When printing on a substrate, the directions are shown by arrow L and W in FIG. 1. Likewise, arrows L and W in FIG. 2 indicate the directions of the length and width when printing on objects.
As noted above, to be able to print letters or other symbols on a substrate, there must be relative movement between the print head and the substrate. Since the substrate moves in the direction of its length, other systems are able to print a string of letters, words or symbols in that direction. By rearranging the locations in which the droplets are placed, these systems can also orient each character so that it faces in the direction of the width of the substrate; that is, the systems can print a short line of characters extending across the width of the substrate. However, since there is no relative movement between the print head and the substrate along the width, a single print head cannot print a string of more than a few characters in the direction of the width.
Likewise, when printing on an object, there must also be relative movement between the print head and the object. The object moves along a conveyor belt in the direction of the length. Other systems that print a string of letters, words or symbols in the direction of the length are known in the art of printing systems. By rearranging the locations in which the droplets are placed, these systems can also orient each character so that it faces in the direction of the width of the object. However, since there is no relative movement between the print head and the width of the object, a single print head cannot print a string of more than two or three characters in the direction of the width.
In addition, because each print head is only capable of printing a single color of ink at any one time, it is impossible for a single printer to create a character or other symbol using a plurality of colors. The present invention permits a personal computer to control a plurality of printers, each containing a different color ink, so that colors may be overlayed to create a multicolor character or symbol.
It is a principal object of the invention to provide a new printing system for printing along a direction other than the length of the printing medium.
It is a further object of the invention that the above be accomplished under the control of a single computer, preferably a personal computer.
More specifically, it is an object of the invention to provide a printing system that uses more than one ink-jet printer, where all the printers are controlled by a single personal computer through a single interface on the computer.